DAQ VXI-SC-1102 Manuál s instrukcemi stáhnout pdf (Strana 31)

Chapter 2 Lab and 1200 Devices

DAQ Hardware Overview Guide 2-4 www.ni.com

Data acquisition timing involves the following timing signals:

•A start trigger is an edge-triggered signal that initiates a data

acquisition sequence. You can supply a trigger pulse either externally

through the I/O connector EXTTRIG input or from software control.

You can enable a hardware start trigger by calling the DAQ function

DAQ_Config or specifying trigger mode in the AI_Start.vi or

AI_Trigger_Config.vi.

•A conversion pulse is a signal that generates a pulse once every sample

interval, causing an A/D conversion to be initiated. This signal can be

generated by the onboard, programmable sample-interval clock

supplied by the 8253 Counter/Timer on the Lab and 1200 device, or

can be supplied externally through the I/O connector EXTCONV*

input. You can select external conversion pulses by calling

DAQ_Config. If you do not want to use external conversion pulses,

you should disconnect the EXTCONV* pin on the I/O connector to

prevent extra conversions.

•A scan interval pulse is a signal that generates a pulse every scan.

The scan clock for interval scanning pulses can be generated by the

onboard, programmable scan-interval counter, or can be supplied

through the OUTB1 pin on the I/O connector.

•A sample counter is used when conversion pulses are generated either

by the onboard sample-interval counter or externally. The sample

counter tallies the number of A/D conversions (samples) and shuts

down the data acquisition timing circuitry when the device has

acquired the desired number of samples.

•A stop trigger is a signal used for pretriggered data acquisition to

notify the Lab and 1200 device to stop acquiring data after a specified

number of samples. Until you apply the stop trigger pulse at the

EXTTRIG input, a data acquisition operation remains in a continuous

acquisition mode, indefinitely writing and rewriting data to the buffer.

You can select pretriggering by calling the DAQ function

DAQ_StopTrigger_Config.

•A timebase clock is a clock signal that is the timebase for the

sample-interval or scan-interval counter. Counter B0 is used to provide

the timebase clock when the interval between samples or updates is

greater than 65,535 µs. The timebase for sample and scan interval is the

same.

See your device user manual for more information regarding these signals.

Note The Lab and 1200 devices use half-FIFO mode by default when doing interrupt data

transfer operations for analog input with rates faster than 1500 S/s. You can select between

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 150 151

Žádné komentáře

DAQ VXI-SC-1102 Manuál s instrukcemi Strana 31